U.S. Pat. No. 5,061,425 discloses a process for producing high modulus, high tenacity polyethylene terephthalate (PET) filament by spinning a solution of PET in a mixed solvent system containing trifluoroacetic acid and dichloromethane through a die and into a coagulation medium containing acetone. This results in the formation of a mixture of acetone, trichloroacetic acid, and dichloromethane. U.S. Pat. No. 4,792,573, U.S. Pat. No. 4,917,845, and U.S. Pat. No. 4,957,945 disclose a technique for producing ultra-high molecular weight polyester resin. One of the techniques disclosed in these patents also results in the formation of a mixture of acetone, trichloroacetic acid, and dichloromethane. In commercial operations it is important to be able to recycle such solvent mixtures to make the process commercially and environmentally feasible. In other words, the organic solvents must be used, collected, separated, and re-used in a closed continuous system.
It is unfortunately not an easy task to separate the three organic solvents present in such mixtures. This is because a trifluoroacetic acid/acetone azeotrope forms making quantitative separation by fractional distillation impossible.